


Room Mate

by boneapptheteeth



Category: Undertale (Video Game)
Genre: Alternate Universe - Soulmates, Bara Sans, Half assed smut, Masturbation, Other, Smut, Unnamed Reader, but not actual smut, but she's really not, i originally wrote the reader to be female so sorry if there are some pronoun slips, just an fyi, just realised that you could misinterpret julia as the reader at first, no consent in that sans is doing bad things in a place where he shouldn't but no people are violated, papyrus and undyne are mentioned??, the gender of the reader is never defined so fellas ladies and non binaries have fun, the reader never actually shows up
Language: English
Status: Completed
Published: 2020-01-29
Updated: 2020-01-29
Packaged: 2021-02-27 08:34:31
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,248
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22460410
Author URL: https://archiveofourown.org/users/boneapptheteeth/pseuds/boneapptheteeth
Summary: Sans needs a place to stay for the night and, luckily, his good pal Julia is there to provide! It's great news that her roommate is gone for a while, which leaves a bed unoccupied for our good boney boi to steal for the night. A totally normal bed that won't make his soul go haywire.What could go wrong?
Relationships: Sans (Undertale)/Reader
Comments: 16
Kudos: 131





	Room Mate

"thanks again for doing this, bud. i dunno how i can repay you." 

"Just stay awake for once during a shift; it's boring watching cameras alone, man." 

Sans and Julia exchange mischievous grins, the skeleton monster's eye lights brightening for a moment before he said his next words, "hey, don't count on it. y'know me - i love sleep so much i could do it with my eyes closed." Julia attempted a peeved expression at the monster's answer, but she couldn't truly hide her amusement. This was expected since Sans usually shot his worst jokes her way during their shifts together and she thoroughly enjoyed most of them - save for the most cringe-worthy quips. 

The two had just entered the human's apartment, standing at the entrance of the abode. Sans didn't usually make a habit of intruding on people's homes, especially since he most often felt uncomfortable in someone else's private territory, but it seemed he would have to make an exception this time. 

Sans usually stayed at the house that he owned with his brother, but there had been some... mishaps... that may have happened during a hang out between Sans's brother, Papyrus, and his fishy best friend, Undyne. Not to say she was suspicious - she was a literally fish, or a fish monster if you will. Though Papyrus did often cause destruction in his excitement, that was nothing on the combined efforts of Papyrus and Undyne; it was as if some doofus combined a chainsaw with a jackhammer and called it a chainhammer (though, the clear better choice for a name was a jacksaw). The two were an unstoppable destructive force and Sans certainly couldn't stop them from altering the brothers' house in a way that called for extensive repairs that most definitely caused the brothers to temporarily evacuate the premises… for at least a day, in order to make the place livable again - more repairs would definitely need to be done much afterwards. Not that Sans tried very hard to stop them from doing said destruction. What could he say, he was soft for his brother... and he was a lazy bastard. 

Undyne had subsequently offered her and her girlfriend's place to stay, he wasn't sure if it was out of kindness or guilt, but he was grateful nonetheless. Though those feelings of gratitude dulled a bit when he realised that the couple only had one guest bedroom. Sans wasn't adverse to sharing a bed with his bro if need be - he loved him, though it was a bit weird as two grown monsters - but the problem was that the brothers were quite large in their own ways. Papyrus was a tall, stalky skeleton who often had to curl a bit to fit most beds, even monster-made ones. And Sans was a slightly lower than average height monster with a wider build, one could call him fat if he weren't all bones. Therefore, due to their respective sizes, the brothers couldn't possibly fit in a single bed. There was always the option of the couple’s couch, which Sans would most likely take because beggars can't be choosers and no way would he let his brother take the much too short for his stature couch, but he wasn't exactly jumping for joy at the thought of an unrestful sleep on a couch he could barely fit on after subsequent nights of overtime leading up to the incident. Sans could sleep anywhere, but that didn't mean he would get good sleep. 

He was so miffed about the idea that he had grumbled it about it to his work buddy, who had perked up with an idea. Julia had offered her place to stay, to which Sans immediately answered with, "uhh, i dunno 'bout that, bud. i know your place is on the small side and couch surfing on a human-sized couch is sure to be more of a pain in the spine than snoozing on a monster-made one." 

The human woman chuckled and proceeded to explain that her roommate was out of town visiting their parents for a few days and she was sure that the other human would most definitely give him permission to use their bed for a night. Plus, she added, her house was closest out of the three in the equation - Undyne's being much farther than Julia's and Sans' from their place of work, so it would be the most convenient. Furthermore, just to drive in her case, she stated that her roommate had a king-sized bed, that they had taken from their parents' house when they moved out, that would be able to fit Sans' stature; at least barely, but definitely better than a couch could. 

"And I know you monsters have those mystical dimensional boxes that store your things so don't even try to make the excuse that you would have to pick up your stuff anyway just to be polite or some shit." 

So, after a quick call to Papyrus to notify him of the situation at hand and a text to Julia's roommate, Sans had agreed to Julia's offer and, after work, the two headed toward the human's apartment. 

"My roomie's anxiety sucks for them, but it's great for getting quick responses - dude's always glancing at their phone and worrying about taking too long to respond. I keep telling them to care less about people but, in this situation, it's great that it took them like, two seconds to respond." Sans chuckled at Julia's words, interest tickled. Julia didn't mention much about her roommate - which was a bit odd since the human talked quite a bit about many aspects of her life - so Sans only knew a few bits about the other human. 

The apartment was fairly small, barely able to fit two humans, and maybe could house a single monster. One on the small side. There was a ratty couch in the side of the room he assumed was the living room, and a stand set in front of it where he deduced a television should have gone. On the other side of the room there was a stove, fridge, sink, and a few cupboards along with some counter space. Near the kitchen area there was a small card table with three fold-out chairs scattered around it. 

Julia noticed him scoping out the place, "Yeah, I know it's not much, but hey, at least you only have to stay in this dump for one night." 

Sans parted his gaze with the tie draped over a chair that he was staring at quizzically to make eye contact with his co-worker, "hey, i really can't complain since you're giving me a bed to stay in. besides, not everyone has the fortune of inheriting riches from a mountain that their civilisation was trapped underneath for centuries. you win some and you lose some, you're just unfortunate." After the monsters had arisen from their underground prison, they had discovered their gold was worth much more than they had exchanged it for in the Underground. Of course, with the new surplus of gold, its value had dropped slightly, but monsters still could get a decent amount of human money for trading in their G. 

The corners of Julia's mouth rose and she pursed her lips in an attempt to hold in her snickers, "Yeah, we can't all be lucky like you, big guy. Monsters obviously have it good." The only reason she could say that without offending Sans was because the two had had talks about the unfortunate entrapment of his race and the subsequent racism they faced soon after their ascent. He knew Julia meant no harm. 

"Anyway, mi casa es tu casa, basically. Well, actually, I know just how much ketchup you can drain. Don't touch the ketchup... or at least leave half the bottle, please? My roommate usually does the shopping - even though we agreed to rotate at first, oops - but since they’re gone, I had to get my lazy ass down to the grocery store and it took me, like, 25 minutes to find the good ketchup. Shit, that's just gonna make you want to drink it more, isn't it?" 

"heheh, yup." Was Sans's distracted answer as his attention wandered over to the object in the dining area once again. It was a tie... covered in chickens? Confused, Julia followed his light of sight and chuckled when she realised what he was looking at. 

"Ohhh, that? That's a little something I bought my roomie after I shot a few of your puns at them and I realised how much they hate puns. It's a hen tie." she explained, eying the skeleton out of the corner of her vision to gauge his reaction. 

Sans stared back curiously at her before looking back to the object, "a hen... tie..?" he furrowed his brow bones before an expression overcame his face that looked as if he were ascending to heaven. 

The next words out of his mouth were painted with enlightenment, "hentai!" he exclaimed excitedly. 

There was a moment of silence before the human in the room burst out in manic laughter, bending over to hold her stomach. Sans watched on with amusement, his grin stretched further than usual. 

Julia's eyes seemed to bug out a bit, "Holy shit! That's the first time I've ever heard someone say 'hentai' like that!! You sounded so happy, oh my fucking god, Sans!" 

The skeleton in question giggled at the wheezing human and the general situation, giddy from the pun and his friend's joy. 

"Well, we've just been standing here like a bunch of dweebs, so let's get your bony butt in bed; I can't wait to get rid of you." Julia smirked before turning to lead Sans to, supposedly, her roommate's room. 

"hey, if it's too hard to admit you miss my presence every moment of the day, i get it. s'pretty embarrassing." 

She laughed, "You wish, loser." 

Sans took that moment to be in his head, to think about why he felt... odd. It really wasn't a bad odd - in fact, it was a kinda good odd, if that made sense - but it was definitely unusual. He felt more content and relaxed than he typically was, which was a difficult feat since he was often tense, feigning a relaxed posture. His soul also felt funny, he couldn't put a phalange on it but it just was off. 

For some reason, with every step he took behind Julia, these sensations only grew. 

They stopped in front of a closed door. 

Julia turned, "Well, here we are! Your home for the night. Just don't fuck anything up and all will be good - my roomie has pretty low standards." 

"heheh, yup, will do." 

She turned to open the door, hand reaching up to the silver handle. It was as if everything was in slow motion. She clasped the handle, turned it and pushed open the door. 

The door was opened and... a rush of pure _scent_ rushed toward him. 

He was stunned, frozen in place. 

Julia didn't seem to notice anything wrong, "Well friend, I'm dead so I'm gonna hit the hay. Wait did I just make a pun? Dead!" she looked at him expectantly but he didn't react, 

"Wow, tough crowd. G'night, dude. Bathroom's down the hall, uh, if you need it." She retired to her own room. 

Sans was... gobsmacked to say the least. The smell coming out of that room was... _delectable_. No wonder he'd been feeling odd ever since he entered the apartment, he was smelling this scent around the place without even realising it. 

He felt a sense of euphoria that he'd never experienced before. 

He took a step into the room. 

Stars, fuck, now the scent wasn't making him feel relaxed, it was doing quite the opposite. Making him feel tense in... _other_... areas. There was a fire burning inside him and his magic was raging. 

Shit, _shit_ , what was happening? 

Though it was dark, Sans could still make out the details of the room with his exceptional night vision. 

The room was quite normal, its only irregularity being its relatively small size, especially in comparison to the large bed within it that took half of the room's space. Its walls were painted a muted yellow and the bed sheets were a slate grey, with various coloured pillows decorating its surface. There was a small desk crammed in the corner with a fold-out chair that was slightly pulled out as if someone had just stood up from it. The room was in an organised chaos - things littered about but in their rightful places. 

Though Sans took time to observe the room, he couldn't really distract himself from the sensations in his soul; the core of his being was anxiously buzzing. 

What was this? Why was this happening?? What the fuck was this scent and why was it affecting him like this??? 

His skull was starting to feel a bit hazy. Maybe this would go away once he got used to this scent, maybe he should just get some shut-socket. Honestly, he was pretty exhausted and he could deal with all this tomorrow. 

Sans took out his phone and proceeded to open his dimensional box and change his clothes. Most often, he didn’t bother to change his clothes before he slept, but if he lent his bed out to a stranger, he wouldn’t be thrilled to learn that they wore their outdoor clothes on his sheets – he was just trying to be mindful of courtesy. After changing into a t-shirt similar to the one he had changed out of, and donning only his boxers on his lower half, Sans was finished with his pre-bed prep. Though monsters didn't create waste in the same way humans did, they did maintain personal hygiene. Albeit, they didn't need to attend to their cleanliness as often. This meant Sans could skip brushing his teeth before bed. Although, he knew that if Papyrus found out, the taller skeleton would lecture him on the importance of upkeep and routine. The other monster was constantly going further than what was needed of him, and though Sans admired that trait in his brother, he'd be damned if he would adopt the same attitude. 

The stout skeleton collapsed on the bed.

Which he learned was a big mistake.

His senses seemed to be overloaded. He should have realized that the scent would be more concentrated on the bed… though, he hadn’t been sure if the smell necessarily belonged to the owner of the room. Now he was sure.

There was no other option, the sweet scent that embraced his rigid body undoubtedly had to have come from the person inhabiting the room – there was no way the scent would be as concentrated otherwise, and concentrated on the bed nonetheless.

Stars, his soul was going crazy, it was insistently tugging and pulsing. It pumped waves of positive feelings and arousal throughout his skeletal form. It was acting as if…

As if he had found his soulmate.

But that was impossible, he would have to meet them in person to know what they were to him. Then again, he’d never heard of a case where a monster had been surrounded by their soulmate’s scent before meeting them. He wasn’t supposed to be driven near insanity by just smelling his soulmate, or at least that’s what he gathered from the soulmate pairs he’d seen. Then again, soulmates were often urged to mate when they first met; it was an instinctual reaction to meeting the person you would create ideal offspring with. With that in mind, it would make sense that a large factor driving monsters to desire to have sex with their soulmate upon first contact would be their scent.

That would also explain the raging magic that had formed in his boxers.

It seemed that Sans was having difficulty controlling his soul’s desires. Fighting his magic forming in preparation to mate was like fighting an uphill battle – though it was all pointless because there was no mate present to even sate his soul’s wants.

Sans lied crookedly on the bed, the piece of furniture barely large enough to support his larger size. He adjusted himself to lay with his skull on the pillow at the head of the bed. He couldn’t help but turn his skull so that his nose cavity was pressed into the pillow underneath him.

Shit, how could he sleep with such a delicious scent engulfing him?

He flexed his toes that just about dangled off of the mattress and he realized that his soulmate was probably about the average size of a human – the tallest human he’d ever met still didn’t hold a candle to his own height. While Sans never really paid much attention to humans, preferring to canoodle with willing monsters during periods such as his heat cycle and when he was bored, but the idea of towering over his squishy, human soulmate? Stars, that really sent a shiver down his spine. He really liked that idea, and thinking of pinning his small human down on the bed he was on and seeing their tiny lips let out a gasp in surprise? Fuck, it really wasn’t helping the burn in his bones, in fact, it was only feeding it.

Shit, shit, shit, he really wasn’t going to get any sleep.

Wasn’t the point of him using this bed to get some proper rest? Though, he couldn’t find it within himself to be upset at the situation he landed in. He had a soulmate! Well, technically everyone did, but it was unlikely one would find theirs.

He couldn’t believe his soulmate was Julia’s roommate; he and the human had been co-workers for a good few years, and he had been narrowly missing his soulmate all this time. Stars, he felt like a fool.

That feeling was further fostered by the fact that he knew what he probably looked like at that moment; a panting, sweaty mess, with bones heated, and a glowing, magical boner in his bone-printed boxers. Wonderful, how the world works, huh?

It was ridiculous how worked up he was over this person he’d never met, when he didn’t even know what they looked like. Fuck, but he didn’t care; what he wouldn’t give to touch their soft skin with his sharp, off-white claws. He’d love to dip the tips of his phalanges into their malleable flesh, but not enough to draw blood – he’d do that with his teeth.

Sans groaned as he imagined the taste of his human’s perspiring skin, and the tang of their ruby life-essence. He’d leave a mark on them, both physically and with magic, so that everyone would know they belonged to him – monster or human. He couldn’t help but growl at the thought of his little soulmate spread out like a feast for him, claimed thoroughly, and only _his_.

The skeleton had never been the possessive type, usually easygoing and flexible, so he wasn’t too sure where all these feelings were coming from. Yet, the thought of giving up his sweet human that he’d never met but would die for to some sick sucker, made him want to rampage and dust anyone between him and his sweetheart. Surprising, since he wasn’t typically violent.

It must have been a soulmate thing, and maybe he’d be more torn up about his sudden change in character, but he was preoccupied with imagining the owner of the scent he was bathing in underneath him.

Sans needed relief more than he ever had in his life (aside maybe during his heats, but it was a different type of desperation), yet he had to contemplate the ethics of masturbating in someone else’s bed. Given, it was his _soulmate’s_ bed, but they didn’t know that they were his. But they would never know of his sins as long as he never left evidence…

Throwing all his common sense out the window and caution to the wind, the monster reached down into his bright blue bone boxers and pulled out his pulsing magic, groaning at the contact between his heated phalanges and his even more heated member.

It wasn’t nearly enough, but it was a reprieve from the agony of doing nothing while his soul begged for a release.

He groaned, beginning to stroke slowly, skull thrown back and sockets closed. He imagined that, instead of his hard bones, it was plush, human fingers surrounding and caressing him. It was never something he’d thought of before, but the idea was becoming more and more inviting the more his soul cried out in pure elation at his imagined world.

Maybe his mate would smirk at him in approval at the sounds he was making (though they were soft, since he was conscious of Julia’s presence across the hall), or maybe their face would be coated in a thick blush at the sinful things they were doing to him. Their touch wasn’t enough though, he wanted to see _their_ reactions to the pleasure he could give them. He’d switch their places and bask in their baffled expression of surprise, chuckling at their pout. He’d bury his skull in their neck and sample their delicious scent from the source, maybe give them a small nibble to foreshadow the claiming he would definitely give them. He bet they’d gasp and then groan at the sensation, letting him pleasure them. He’d chuckle and trace his phalanges down their squishy body, making sure to memorise each and every curve. He’d undress them slowly, communicating how much he wanted them through his bright gaze, and they’d shiver in want. Sans would finally be able to bask in their beautiful, flawed form; he’d love each and every flaw that they had since they all worked to shape his soulmate’s character.

He wouldn’t be able to hold himself back any longer, diving down to pleasure his mate’s most sensitive spots, using his teeth and summoned tongue to give his full attention to the space between their legs. It would be pure ambrosia, he’d want to never stop, moaning into his mate’s skin at the sheer taste of them. Oh stars, if smelling them was this intense, he could only imagine he’d dust on the spot at the pleasure tasting them would cause his skeletal body to undergo! Fuck, the noises they would make would be the most hypnotizing music, and he would never want the moment to end. Their climax on his tongue would be the most intense experience of his life, and he would simultaneously be blissed out as well as disappointed it was over. Their pleasured screams would be imprinted in his skull for all of eternity, and he’d forever crave the feeling of his sweet mate’s legs around his bones once again.

They would smile at him, their face red and sweaty, and he would be reminded of the hard magic in his pants. Growling, he’d pounce on his soulmate, and they’d laugh at his enthusiasm, welcoming him with open arms that would wrap their way around his neck. Sans would kiss their pink lips and lead himself inside of their warm body, unable to hold back his snarls and growls when his member began to be embraced by his mate’s velvety canal. He would sheath himself completely, kissing away his sweetheart’s whimpers, and begin pumping at a steady pace. The experience would be as ascendant as heaven, but as hot and passionate as the depths of hell. Sans would indulge in his soulmate’s gorgeous body, and drink in their cries of ecstasy. He’d lose control of his inhibitions in his pleasure, gaining speed, and slamming into his small mate, **his** mate, until… until…

“f-fuck..!” Sans had been envisioning the thorough boning he’d give to his soulmate so vividly that he had forgotten where he was – laying in the bed of the person in his mind and stroking his cock fervently, that is.

Gritting his teeth, the skeleton attempted to hold in any more sounds that may escape him as he climaxed, blue-tinted cum spurting out of his blue shaft and onto his hand. He imagined sinking his fangs into his mate’s skin as he finished, his soul urging him to do just that. The thought that he wished he had released inside him mate crossed his mind before he came down from his high.

He lay panting and sweaty on the barely big enough bed, that belonged to his newly-discovered soulmate that he’d never met, after furiously masturbating. How bizarre. He knew it was wrong and that he shouldn’t have done what he did – it was vile, creepy, and incredibly invasive – but he couldn’t come to wholly regret what he did. Perhaps he partly felt that way because he still wasn’t fully relieved; after all, his soul was begging for him to find and fuck his little mate instead of his hard hand. And he was inclined to do just that, well, maybe just the finding part first. Luckily, it wasn’t looking to be too difficult, since all the pieces were in place.

He’d have to have a good talk with Julia the next morning.

…Hopefully she hadn’t heard him.

And so, slightly uncomfortable and warm, Sans shut his eye sockets and had one of the most relaxing sleeps of his life.

Well, that came _after_ he got up to wash his sticky phalanges. But after that, Sans had a restful slumber with the knowledge that he would soon meet his sweet mate. 

**Author's Note:**

> sans: hey so i think i should wash your roommate's sheets, y'know, for cleanliness  
> julia: hey man, it's good, i was gonna do it this afternoon anyway, i gotchu  
> sans: thank fuck  
> julia: ...what? 
> 
> hey so this story is an attempt to get my out of my writing funk. i literally haven't updated saccharine hope in like two months cause i'm a turd, but also we're in kind of a boring filler-ish part. i don't remember where i got this terrible idea, but here you go? I had been wanting to write a gender ambiguous reader smut piece for a while to be more inclusive but hadn't done so cause it's just so much harder, but also it's easier to make a scene sexier when you go into the nitty gritty of genitals and crap. props to the ppl who write smut with gender ambiguous characters and make it good. 
> 
> also the reader's roommate is named julia because for some reason there's been a lot of julias in my life.


End file.
